Papua New Guinea is one of the most culturally diverse countries in the world; 852 languages are listed for the country, of which 12 have no known living speakers. Most of the population of over 7 million people live in customary communities, which are as diverse as the languages. It is also one of the most rural, as only 18 percent of its people live in urban centres. The country is one of the world's least explored, culturally and geographically; many undiscovered species of plants and animals are thought to exist in the interior, as well as groups of uncontacted people.